1. Field of the Invention
The present invention relates to an oscillating mold for continuously casting slabs, preferably of steel, with immersion outlet and continuous casting powder.
2. Description of the Related Art
Continuous casting takes place particularly in sizes with a thickness range of between 20 and 250 mm, preferably 40 to 150 mm (thin slabs), and with widths of between 500 and 3,300 mm, preferably 500 to 1,800 mm, with casting speeds of at most 10 m/min.
Previously known slab molds or thin slab molds which are open by providing a funnel or trough in the casting meniscus can be divided into the following groups and have the following advantages and disadvantages.
German Patent 887 990 describes a funnel-type mold with a rectangular mold outlet opening, wherein the mold consists of a single unit and does not have short side walls which are independent of the long side walls. This mold does not make it possible in the case of different continuous casting speeds and steel qualities to adjust the conical shape of the short side walls to the shrinkage dimension of the strand in the width direction over the height of the mold and it also does not make it possible to cast different strand widths. In addition, there is the danger that the strand shell will be jammed in the mold which leads to rupture of the strand shell as it is being discharged.
German Patent 34 00 220 describes a funnel-type mold with long side walls and short side walls in which laterally next to the funnel-shaped pouring area is arranged a parallel area which corresponds at least to the thickness of the cast strip or the thin slab. This mold eliminates the disadvantages of the mold according to the above-described German Patent 887 990.
Japanese Patent document 58-86906 describes a mold which is concavely shaped independently of the shape of the immersion outlet and has a residual conical shape at the mold outlet opening. Simultaneously, the extent by which the concave shape is reduced over the mold length is greater than the shrinkage of the slab over the mold width, so that the conicality of the short side walls becomes negative or the strand width is greater at the mold outlet opening than in the casting meniscus area. In addition, this solution does not ensure a uniform slag formation over the strand width because the active strand thickness is not uniform at the meniscus for melting the casting powder. This non-uniform slag formation can also be observed in German Patent 36 27 991.
German Patent 41 31 829 describes a four-plate thin slab mold which has a concave shape in the area of the smallest slab width. The maximum opening in the casting meniscus area and in the slab middle is 12 mm for each 1,000 m slab width.
This mold shape has the disadvantage that in the area between the long side walls of the mold and the immersion pipe, which is very narrow as compared to the area outside of the immersion pipe (at most 2.times.0.25 slab thickness+12 mm), a deficiency of casting slag as well as a deficiency of fresh melt occurs which lead to an increased thermal flux and shrinkage behavior as well as to undercooling and bridge formation between the strand shell and the immersion outlet. These disadvantages result in a high susceptibility to longitudinal cracks at the slab surface in the area around the slab middle.
German Patents 44 03 045 and 44 03 050 describe concave mold shapes, but no statements are made concerning a relationship between the concave mold shape and the outer and inner immersion outlet shapes. This missing optimization of the shapes relative to each other results in problems in the thermal flux over the mold width and mold height as well as in the steel flow in and below the casting meniscus which, in turn, increases the danger of the formation of longitudinal cracks.
In European Patent Application 0 109 357 A1, the immersion outlet or immersion pipe are not taken into consideration when selecting the concave mold shape. In addition, this European Patent application deals with molds for casting aluminum with the use of electromagnetic fields, i.e., the strand does not have any contact with the mold when the strand shell is formed.
Moreover, no casting powder is used and the mold does not oscillate. In addition, casting is not carried out continuously, but so as to rise in a type of block casting mold.
In addition to the thin slab molds discussed above, the classic slab mold with the rectangular dimensions of, for example, 200.times.2,000 mm, shall be discussed. Aside from the fact that the casting speed is at most 2 m/min and the thermal flux and, thus, the shrinkage is only about 1 MW/m.sup.2 and about 1%, this standard mold system has the following deficiencies in spite of a relatively thick slag film between the strand shell and the mold of, for example, 1 to 2 mm thickness.
non-uniform slag formation over the strand width in the area of the immersion pipe; PA1 undercooling of the steel in the area of the immersion pipe as compared to the area next to the immersion pipe; PA1 impairment of the shrinkage of the strand shell in the horizontal direction by the parallel mold shape, particularly in the case of wide slab sizes. PA1 the casting capacity, PA1 the inner and outer shape, PA1 the flow cross-sections, PA1 the outlet openings in size and arrangement, and PA1 wall thickness (maximum casting time, number of melts in sequential casting) PA1 uniform slag formation over the slab width, PA1 uniform and quiet bath movement, PA1 low-friction and uniform shrinkage of the strand shell over the width of the slab, PA1 casting of different slab widths in one mold (large adjustment range), and PA1 adjustment of different conical positions of the short side walls by control and by regulation.